Generally, a finger clip oximeter according to the prior art includes an upper case and a lower case which are connected with each other by a pivot, can be rotated around the pivot relatively and be separated by a certain distance from each other. The upper and lower cases apply a clamping pressure to a nail of a measured finger by a coil spring.
However, when the finger clip oximeter clamps the nail to perform oximetric measurement, the upper and lower cases are opened a certain angle with respect to each other necessarily. After the upper and lower cases are opened, light will enter from a side thereby to influence the measurement result in case that the light is strong. Different persons have different sizes of fingers, therefore, the angles which the upper and lower cases are opened with respect to each other are different and the influences owing to light entering from a side are different as well. Accordingly, the finger clip oximeter is hard to perform calibration on fingers with various sizes in advance, so that a light path offset occurs easily during its practical use resulting in a measuring error.
In addition, in the finger clip oximeter according to the prior art, a finger clamping portion of the upper and lower cases applies a non uniform force to a finger along the length of the finger, and the smaller clamping force exists in the location which is more away from the hinged pivot. Because different users are different largely in sizes of fingers, the clamping portion of the finger clip oximeter according to the prior art can only be defined within a prescribed range of size, and it is impossible that any specific finger clip oximeter according to the prior art is applicable to a finger which is too thick or too thin. Therefore, the range in which the finger clip oximeter according to the prior art can be applied is limited. Further, for a user with thicker fingers, the user's fingers are not comfortable when he uses the finger clip oximeter according to the prior art.
Since the finger clip oximeter according to the prior art is limited in its structure, a portion where the cases contact with a finger can not be cleaned conveniently and thoroughly. Therefore, there is a risk of cross propagation of bacteria among different users in use.
Also, the finger clip oximeter according to the prior art is complicated in structure and difficult to be assembled.